U.S. patent application number 10/275675 was filed with the patent office on 2003-08-21 for process for the purfication of flue gas.
Invention is credited to de Jonge, Robert Jan, Kleut, Dirk Van De.
Application Number | 20030154858 10/275675 |
Document ID | / |
Family ID | 8171462 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030154858 |
Kind Code |
A1 |
Kleut, Dirk Van De ; et
al. |
August 21, 2003 |
Process for the purfication of flue gas
Abstract
The present invention is directed to a process for the
purification of flue gas, wherein flue gas is contacted with a
carbonaceous material, said carbonaceous material comprising the
solid carbonaceous residue of synthetic rutile production from
titaniferous ores.
Inventors: |
Kleut, Dirk Van De;
(Hoogland, NL) ; de Jonge, Robert Jan; (Bussum,
NL) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN & LEBOVICI LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Family ID: |
8171462 |
Appl. No.: |
10/275675 |
Filed: |
April 11, 2003 |
PCT Filed: |
May 3, 2001 |
PCT NO: |
PCT/NL01/00338 |
Current U.S.
Class: |
95/133 ;
95/134 |
Current CPC
Class: |
Y10S 95/901 20130101;
C22B 34/12 20130101; C22B 7/02 20130101; B01D 2253/102 20130101;
B01D 53/04 20130101; B01D 2258/00 20130101; Y02P 10/20
20151101 |
Class at
Publication: |
95/133 ;
95/134 |
International
Class: |
B01D 053/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2000 |
EP |
00201649.1 |
Claims
1. Process for the purification of flue gas, wherein flue gas is,
contacted with a carbonaceous material, said carbonaceous material
comprising the solid carbonaceous residue of synthetic rutile
production from titaniferous ores.
2. Process according to claim 1, wherein said carbonaceous material
is injected into the flue gas to be purified.
3. Process according to claim 2, wherein the said carbonaceous
material is removed from the flue gas after sufficient contact time
for adsorbing contaminants from the flue gas.
4. Process according to claim 1-3, wherein the flue gas is cooled
to a temperature between 0 and 500.degree. C., before contacting it
with the said solid carbonaceous material.
5. Process according to claim 1-4, wherein flue gas originating
from waste incinerators, the metallurgical industry, the metal
recovery industry, power plants or cement plants is treated.
6. Process according to claim 1-6, wherein dioxins, furans and
mercury compounds are removed from the flue gas.
7. Process according to claim 1-6, wherein the said solid
carbonaceous material is contacted with the flue gas in dry state,
wet state and/or in combination with lime.
8. Process according to claim 1-7, wherein the said carbonaceous
material is sieved, purified and/or ground, prior to use.
9. Use of a solid carbonaceous material comprising the solid
carbonaceous residue of synthetic rutile production from
titaniferous ores, in the purification of flue gas.
Description
[0001] The invention is directed to a process for the purification
of flue gas, wherein flue gas is contacted with a carbonaceous
material.
[0002] Various industrial processes produce vast amounts of flue
gas streams containing environmentally hazardous substances, such
as fly ash, acid gasses, NOx, dioxins, furans, and heavy metal
compounds. Examples of such industries are waste incinerators
burning various feeds (municipal waste, clinical waste, hazardous
waste), the metallurgical industry, the metal recovery industry,
power plants, cement plants and the like.
[0003] In order to reduce the emission of hazardous substances,
many industries are obliged to clean up their flue gasses before
ventilation in the environment. Depending on the nature of the
pollutant, various techniques have been developed to clean up the
flue gas. For example, fly ash can be removed with electrostatic
precipitators (ESP), fabric filters (FF) or wet scrubbers. Acid
gasses are mostly bound to alkaline compounds, either in a (semi-)
dry system with spray dryer adsorbers (SDA), or in wet systems
using scrubbers. Many flue gas cleaning installations have been
build containing these basic components.
[0004] For the removal of dioxins, furans and mercury compounds
from flue gas often additional measures have to be taken in order
to comply with the current emission limits. Mostly, the flue gasses
are brought into contact with an adsorbent to bind these
compounds.
[0005] A well-known method to remove dioxins, furans and mercury
compounds is to inject a powdered adsorbent in the ducts of a flue
gas cleaning system, after which hazardous compounds adsorb onto
the adsorbent. In subsequent parts of the installation the spent
adsorbent is removed from the flue gas in a particle collection
system. The collection of the adsorbent is often performed in
existing ESP, FF or wet scrubbers, which makes this technology
especially suited for existing flue gas cleaning installations. A
vast amount of patents have been granted describing various flue
gas cleaning installation modifications applying powdered
adsorbents for flue gas cleaning.
[0006] The conditions under which adsorbents are applied depend to
a large extent on the nature of the industrial process generating
the flue gasses and on the modification of the flue gas cleaning
installation.
[0007] In general, flue gas consists of fly ash and various gasses
and volatile compounds, such as nitrogen, oxygen, carbon dioxide,
nitrogen oxides, water, carbon monoxide, sulphur dioxide, and
various acid gasses. The precise composition of the flue gas is
determined by the nature of the process generating the flue gas and
can vary significantly in time. A suitable adsorbent must be able
to withstand these variations of the flue gas composition.
[0008] The maximum temperature at which powdered adsorbents can be
used is partly determined by the maximum operating temperature of
the particle collection system. For ESP and FF the maximum
operating temperatures are typically 450.degree. C., respectively
300.degree. C. In wet scrubbers the maximum operating temperature
is always below 100.degree. C. The maximum application temperature
is preferably kept below 250.degree. C. to prevent the formation of
additional dioxins due to the so-called de novo synthesis
route.
[0009] Various adsorbents are used for the cleanup of flue gas.
Commonly reported adsorbents for this application are activated
carbon and activated lignite cokes.
[0010] The adsorption capacities of activated carbon and activated
liguite cokes for dioxins and furans can be extremely divers,
depending amongst others on the nature of the raw material and on
the method of production. Usually, the carbon types used in flue
gas cleaning are produced from raw materials like peat, coal, or
lignite, produced by steam activation processes. Alternatively,
carbon adsorbents are produced by miffing reactivated granular
carbon or activated carbon waste. The PAC types based on
reactivated carbon or on activated carbon waste generally have a
varying quality due to the varying quality of the raw material.
[0011] The main properties determining the quality of activated
carbon for flue gas cleaning are the adsorption properties and the
ignition properties.
[0012] The adsorption properties are mainly determined by the pore
structure and by the particle size distribution of the powdered
activated carbon. The pore structure of the carbon is defined by
the nature of the raw material and by the process conditions during
activation. A suitable activated carbon preferably contains a high
micropore volume for a high adsorption capacity, next to a high
mesopore volume for a rapid transport of the adsorbates to the
adsorbing pores. The particle size distribution is primarily
determined by the quality of the milling equipment.
[0013] When applying powdered carbon under oxidising conditions at
elevated temperatures as in flue gas, the possibility of ignition
of the carbon has to be taken into account. Typically, the
temperature in the ESP or FF of the flue gas cleaning system ranges
from 100 to 200.degree. C. In some cases the temperatures are even
higher.
[0014] Ignition of carbon adsorbents is usually first observed in
the dust collection sections of an ESP or a FF, since on these
spots warmed up carbon can accumulate. Under sufficiently severe
conditions in principle all carbon adsorbents can eventually
ignite, resulting in undesired excessive temperature increases.
Changes in the design of the installation can reduce the ignition
hazard. Choosing the proper carbon adsorbent can reduce the
ignition hazard as well.
[0015] In general the ignition properties of an activated carbon or
other material used in flue gas cleaning systems are determined
using a standard ignition test. Such tests are defined in the
Recommendations for the transport of dangerous goods, 9th revised
edition, United Nations, 1995, parts 14.5.5 and 33.3.1.3.3.
[0016] Next to the adsorption and ignition properties, secondary
properties such as material availability and production costs also
determine the suitability of an adsorbent for flue gas
cleaning.
[0017] It is an object of the present invention to provide an
alternative to the presently used powdered activated carbon,
whereby the ignition characteristics of the material are
improved.
[0018] It is also an object of the present invention to provide a
carbonaceous material suitable for flue gas purification, wherein
the material has an improved balance of properties in relation to
adsorption characteristics and ignition behaviour.
[0019] The present invention is based on the surprising discovery
of a material that meets these objects, when applied in flue gas
purification. Surprisingly, a new carbonaceous adsorbent material
was found having a pore structure that is likely superior to that
of activated carbons commonly used for flue gas cleaning. The new
material is produced as a by-product in the synthetic rutile
production industry and has excellent ignition properties. These
combined properties make this new adsorbent especially suitable for
flue gas cleaning.
[0020] The said solid carbonaceous material is produced as waste
product during the production of synthetic rutile from titaniferous
ores (ilmenite, leucoxene, or slag). During the production of
synthetic rutile, carbon is used for the chemical reduction of iron
within the titanoferous minerals, possibly in combination with
chlorine. The reduced iron is subsequently removed from the
minerals to obtain synthetic rutile. (See Ullmann's Encyclopedia of
Industrial Chemistry, Sixth Ed,; 199 Electronic Release, Wiley-VHC,
Weinheim (DE) on Titanium Dioxide, .sctn. 2.1.2.2. Synthetic Raw
Materials)
[0021] After recovery of the synthetic rutile from the solid
material a carbonaceous waste product remains, which has been found
to have a pore structure corresponding to the pore structure of
activated carbons that are suitable for adsorption of contaminants
such as dioxins, furans and mercury compounds from flue gas. If
necessary the material can be purified, sieved and/or ground to
obtain the optimal properties. More in particular, the particle
size may need to be regulated, depending on the type of system
used. Generally the material is modified to have a particle size
between 1 and 100 .mu.m.
[0022] It is possible to combine the said carbonaceous material
also with other solid materials, such as activated carbon and the
like. However, it is preferred that the amount of material added is
subordinate in amount to the said solid carbonaceous material.
[0023] The carbonaceous material can be used in the same manner as
the presently used powdered carbons, by injecting them at a
suitable location in the flue gas. This can be done in the dry
form, as wetted material and/or in combination with alkaline
materials, such as lime to remove acidic substances from the flue
gas. After the material has adsorbed the contaminants, it is again
removed from the gas, for example by ESP or FF.
[0024] The flue gas has generally been subjected to some treatment
prior to the introduction of the carbonaceous material, such as
cooling to recover some heat from it, removal of fly ash, and the
like. More in particular, the flue gas may be cooled to a
temperature between 0 and 500.degree. C., before contacting it with
the said solid carbonaceous material.
[0025] The invention is now elucidated on the basis of the
following examples, which are not intended to limit the scope of
the invention.
EXAMPLE 1
[0026] The pore structure of activated carbons is generally divided
into three major size ranges: micropores (pore radius<1 nm),
mesopores (1 nm<pore radius<25 nm), and macropores (ore
radius>25 nm). The respective pore volumes are generally derived
from adsorption experiments with standard adsorbates (micropores
and mesopores), or from mercury porosimetry (macropores and larger
mesopores). With activated carbons used for the purification of
gasses, the micropores and the mesopores (adsorbing pores) are
generally used for adsorption of adsorbates, whereas the macropores
and larger mesopores (transporting pores) are used for transport of
adsorbates from the surroundings to the adsorbing pores. A suitable
activated carbon for flue gas cleaning contains both adsorbing
pores and transporting pores in sufficient amounts, to provide
optimum adsorption capacity and fast adsorption kinetics. For
powdered activated carbon types the macropores have largely
disappeared due to the mailing process.
[0027] A commonly accepted analytical parameter for activated
carbon is the so-called iodine number. The iodine number is the
amount of iodine adsorbed onto activated carbon (in mg iodine/g
carbon) in equilibrium with a 0.02 N iodine solution The test
method has been described extensively in ASTM D 4607-86. The iodine
number of activated carbon is related to its micropore volume. An
alternative parameter indicating the micropore volume of activated
carbon is the equilibrium butane adsorption capacity when the
carbon is brought into contact with dry air containing 0.24 vol %
butane. The iodine number is thus related to the volume of the
adsorbing pores.
[0028] A parameter indicating the combined pore volume of larger
mesopores and small macropores is the molasses number. The molasses
number is defined as the number of milligrams activated carbon
required to achieve the same decolorizing effect as 350 mg of a
standard carbon, determined using a standard molasses solution by a
standard procedure. Due to the large size of the molasses molecules
only large pores can be entered, therefore, the molasses number is
an indication for the volume of the transporting pores. In this
case, the molasses number decreases as the transporting pore volume
increases.
[0029] Table 1 contains typical iodine numbers and the molasses
numbers of several activated carbon types that are commonly used
for flue gas cleaning, as well as those of the carbonaceous residue
produced in the synthetic rutile production process. Based on these
values, the adsorption properties and adsorption kinetics of the
carbonaceous residue are more favorable for flue gas cleaning
compared to the currently applied carbon types, because both
adsorption and transport pore volumes are higher.
1TABLE 1 Typical Iodine numbers and Molasses numbers of various
activated carbons used for flue gas cleaning, and of the
carbonaceous residue material. Iodine number Molasses number Carbon
type [mg/g] [a.u.] Darco FGD 550 400 NORIT GL 50 700 475 NORIT SA
Super 1050 200 Carbonaceous residue 1200 150
EXAMPLE 2
[0030] The auto-ignition hazard of stationary activated carbon
layers can be assessed by determining the so-called critical
ignition temperature (CIT). The test method for determining the CIT
of powdered activated carbon is similar to a test mentioned in the
"Recommendations on the transport of dangerous goods, issued by the
United Nations", section 14.5.5 (ST/SG/AC. 10/1/Rev.9). This test
is designed to establish whether or not self-heating substances can
be transported in bulk. In the UN-test it is determined if a carbon
sample in a 1 liter cube (10.times.10.times.10 cm) auto-ignites at
a fixed temperature of 140.+-.2.degree. C. An elaborate description
of this test can be found in the above-mentioned manual.
[0031] The CIT test method is in principal identical to the UN test
method, only the temperature at which the sample is tested is made
variable. Depending on the outcome of the first test at a
pre-selected temperature, a new test temperature is chosen and a
fresh carbon sample is tested. This is repeated until the highest
temperature at which no ignition took place and the lowest
temperature at which ignition did take place are about 10.degree.
C. apart. The CIT is defined as the average of these
temperatures.
[0032] Table 2 contains the CIT values of several activated carbon
types that are commonly used for flue gas cleaning, as well as that
of the carbonaceous residue produced in the synthetic rutile
production process. The data in table 2 clearly indicate that the
CIT of the carbonaceous residue is significantly higher than that
of the regular flue gas cleaning carbon types.
2TABLE 2 Typical critical ignition temperatures (CIT) and average
particle size of various activated carbons used for flue gas
cleaning, and of the carbonaceous residue material. Particle size
(d.sub.50) CIT Carbon type [.mu.m] [.degree. C.] Darco FGD 14 240
NORIT GL 50 17 250 NORIT SA Super 7 270 Carbonaceous residue 33
330
* * * * *